1. Field of the Invention
The present invention relates to a method and system for controlling the gain and offset in radiation measurement apparatus.
2. Description of the Related Art
With radiation measurement apparatus having a scintillator responsive to incidence of radiation to produce scintillations and a photomultiplier (PMT) that converts the produced scintillations to electrical signals, stable radiation measurement, for example, gain control of the PMT is very important in improving the accuracy of radiation measurement.
However, with conventional radiation measurement apparatus, since the gain control is performed manually, it is not easy to control the PMT gain with high accuracy.
A method of controlling the gain of the PMT can be devised in which the PMT is irradiated with standard light produced by a light emitting diode (LED) and the output of the PMT is fed back to the LED. In this case, it is desirable to measure the standard light a plurality of times during radiation measurement. However, when the standard light is measured during radiation measurement, the radiation will also be detected at the same time. That is, when the radiation falls on the scintillator during emission of the standard light, scintillations produced by the scintillator will be detected by the PMT together with the standard light. As a result, the stable gain control of the PMT cannot be attained, lowering the accuracy of the radiation measurement.
Here, by way of example, a method can be devised in which the scintillations may be neglected by irradiating the PMT with standard light having a high energy level as compared with the scintillations. However, measurement conditions for the standard light and those for the scintillations are different from each other. This makes the proper gain control for the PMT impossible.
In view of the above, a device is desired which can perform the stable gain control in radiation measurement apparatus.